1. Field of the Invention
The present invention relates generally to the testing and assembly of integrated circuit devices. Specifically, the present invention relates to a method and apparatus for non-permanently, or temporarily, connecting integrated circuit devices to a substrate.
2. State of the Art
Some types of integrated circuit devices are typically comprised of a semiconductor die attached to a leadframe. An encapsulant material, such as plastic or ceramic, encases the semiconductor die and a portion of the leadframe to form an integrated circuit (IC) package. The semiconductor die has a plurality of bond pads on the active surface thereof having at least one conductive lead connected to at least one bond pad of the semiconductor die. Typically, another portion of each lead of the leadframe extends from the encapsulant material of the integrated circuit package to form an external lead for electrically connecting the IC package to other devices. Integrated circuit packages having a leadframe construction include a thin small-outline package (TSOP) and a small-outline J-lead package (SOJ). Methods of fabricating integrated circuit devices using leadframe construction are well known in the art.
Another common type of integrated circuit package is the ball grid array package (BGA). A ball grid array package is generally comprised of a bare semiconductor die or encapsulated semiconductor die, each type semiconductor die having a plurality of external leads in the form of conductive spheres, such as solder balls, electrically connected to the bond pads located on the active surface of the semiconductor die. The conductive spheres are typically arranged in a two-dimensional array on one surface of the semiconductor die. Methods for fabricating BGA devices are well known in the art.
Integrated circuit devices are commonly assembled into multi-chip modules. Generally, a multi-chip module (MCM) includes a mounting substrate, such as a printed circuit board, having a plurality of packaged integrated circuit (IC) devices mounted thereto. Electrical communication among the IC devices, and between the IC devices and other external devices, is established by conductors on the MCM substrate. The conductors may be conductive traces fabricated on the surface of, or internal to, a printed circuit board. Methods for fabricating printed circuit boards having conductive traces, as well as other types of substrates having conductors thereon, are well known in the art.
The two-dimensional pattern of spherical balls on a BGA device, or the arrangement of external leads on a TSOP or SOJ package, forms what is commonly referred to as a footprint. Generally, the substrate of a multi-chip module has a pattern of conductive traces that forms a plurality of footprints corresponding to the footprints of those IC devices that are to be assembled into the MCM. The external leads of IC devices such as TSOP and SOJ packages may be permanently electrically connected to a corresponding footprint on the MCM substrate using solder or conductive epoxy. The array of spherical balls of a BGA package may be attached to a corresponding footprint on the MCM substrate using a flip-chip bonding process in which the solder balls are reflowed in order to establish a permanent electrical connection between the ball grid array and the corresponding footprint on the MCM substrate. Methods for permanently attaching IC devices to other substrates are well known in the art.
Assembled multi-chip modules may be subjected to a series of tests, such as burn-in and other electrical testing. If the MCM fails a test, the IC devices causing the failure must be removed and replaced. However, the process of removing a bad IC device, and attaching another IC device, can itself cause damage to the MCM. In order to remove an IC device from the MCM, the permanent electrical bonds between the IC device and the MCM substrate must be severed. Severing the permanent electrical bonds may cause damage to the MCM substrate and conductive traces, damage to the leads and electrical bonds of the remaining IC devices on the MCM substrate, and heat-induced damage to both the MCM substrate and remaining IC devices resulting from the reflowing of solder used to effect the permanent electrical bonds.
Prior to assembly into a multi-chip module, individual IC devices are routinely tested at the component level. It is often desirable to attach an IC device that has failed a component level test—a known “bad” device—to an MCM substrate in order to observe the operating characteristics of the MCM with a known bad device, and to observe the operating characteristics of the known bad device at the module level. Typically, once the known bad device has been tested at the module level, the known bad device is removed from the MCM. However, this process of removal again subjects the MCM substrate to potential damage.
Thus, in order to alleviate the potential for damage to a multi-chip module resulting from the severing of permanent electrical connections between the MCM substrate and attached IC devices, a need exists for a method and an apparatus for temporarily attaching IC devices to an MCM substrate using non-permanent electrical bonds. Further, because the design and structure of both multi-chip modules and IC devices varies widely, a need exists for a method and an apparatus for creating non-permanent electrical bonds between an IC device and an MCM substrate that is easily adaptable to different types of IC devices and multi-chip module configurations.